This invention relates to manhole cover supports for emplacing over and raising the effective grade of an existing manhole cover receiving structure such as the usual cast iron manhole cover frame, and more particularly to manhole cover supports having gaps in their lateral keepers for the cover, especially those cover supports that are polygonal in plan.
For simplicity the term "existing manhole cover receiving structure"is used here to refer to the existing, i.e., fixed-in-place frame or other seating receptacle for a removable cover or grating that covers an access hole (i.e., hand hole, tool hole, manhole, catch basin or the like). The term "manhole cover" is used to refer to the removable cover or grating over the access hole. The resulting assembly of a receiving structure and a manhole cover ordinarily is intended to bear vehicular traffic. The term "manhole cover support" or simply "cover support" here means a structure that fits over the existing manhole cover receiving structure, raises its grade, and thereby accommodates a cover or grating at the new elevated grade. The access hole covered is a utility enclosure serving, e.g., an electric, gas, water, sewer or storm drainage system.
Ordinarily the instant cover support finds its use when a roadway such as a street or highway is resurfaced with a layer of paving material. Typically asphalt concrete is overlaid or repaved to establish a higher grade. It then is advantageous to mount the inventive cover support atop the existing manhole receiving structure. Prior art on manhole cover supports and manhole cover frames can be found in U.S. Pat. Nos. 4,281,944, 4,236,358, 3,968,600, 3,773,428, 4,097,171, 4,302,126, 3,891,337 and 1,987,502. The first four of these are for inventions of the applicant.
Axle loads up to 40,000 pounds must be resisted by many of these cover supports as well as serious impact loads from vehicles and snow plows, a variety of temperature effects, steam leaks, spillage, etc., without permitting a hazardous dislocation of the cover support or its cover. Often it is desirable also to cushion the cover a bit for resisting wear or reducing noise, or to seal the cover and its cover support against a substantial and possibly overloading infiltration of surface water, e.g., storm drainage that otherwise would enter a sanitary sewer system at various manhole locations. Adjustability of the cover support in peripheral dimension and height also is desirable for accommodating the wide range of specifications to be met.
Installing, adjusting, loading and unloading and otherwise handling manhole cover supports and removing the covers therefrom usually is done with powerful and indelicate tools such as picks, pinch bars, crowbars, tongs, heavy hooks and the like. Deformation of the cover support can occur, particularly about its upper edge which is nearest the road surface. Also, the upper edge usually is the handiest area for applying lifting and other tools. Deformations along the top never are good, and they can render the opening of the support unfit for service. Hence, overall ruggedness and stiffness against deformation, especially at or near the top rim, and resistance to displacement are major concerns about manhole cover supports.
On the other hand, a relatively light construction of the cover support, in comparison to the usual ponderous cast iron frame that usually initially supports the manhole cover when the first paving is laid, can be very desirable, provided, however, that an inordinate amount of the ruggedness, stiffness, and resistance to displacement or dislodgement is not sacrificed. Usually a main place for weight reduction is in the lateral keeper for the cover. Another place is in the base of the cover support. Clearly, the economics of manufacture, handling and installation all are generally in favor of lower weight. A relatively thin wall keeper would normally be of steel; it is rarely more than about 0.1 inch (12 ga.) thick and usually is less.
The instant cover support is an improvement in a cover support having gaps in the lateral keepers for the cover, particularly those supports of the first, third and fourth parent applications referred to above. The first of these was for a polygonal cover support having adjustable joints at the corners for manipulating the peripheral dimension and the base pressure against reaction surfaces. The third and fourth of these call for hollow wale portions substantially coextensive with the upper part of the cover keeper portion of a metal manhole cover support for stiffness of the relatively light wale and for an improved, more easily made wale of that type.
The instant invention renders the upper parts of the manhole cover support mutually bracing. This imparts greater ruggedness, particularly where those parts are made of fairly thin metal such as 12 gauge (0.1 inch thick) mild steel.
Additionally, this improved cover support can be adapted readily, like its cover supports, of its parent applications, to be sealed off against water infiltration and to cushion the cover. Its base can be made adjustable as to outer perimeter if desired.